A number of sharpening assemblies exist for sharpening or grinding knives, cutlasses, scissors and similar cutting tools. The difference between such sharpening assemblies lies in the amount of grindstones used as well as in the arrangement thereof inside the casing or container covering the sharpening assembly.
The demand for a sharpening assembly that is simple to build and use, as well as of reduced cost, has been gradually increasing in the consumer market. Examples of such sharpening assemblies are described in U.S. Pat. Nos. 2,775,075, 2,898,709, 5,735,732 and 6,398,633, Canadian Patent 1,124,080, and Brazilian Patent Applications PI 0400199-0, PI 0401761-7 e PI 0401928-8.
U.S. Pat. No. 2,775,075 shows a sharpening device having a fixed grindstone, positioned perpendicularly to the base, attached to an engine moving the same. In that patent, the grindstone is accessible from the device outer side through a sharpening V-shaped opening, which results in an extra disadvantage, since the user may inadvertently come into contact with the moving grindstone. The sharpening motion is performed in the upper portion of the casing. In the opening a V-shaped guide arrangement is provided that is responsible for keeping the tool to be sharpened at a predetermined angle to the grindstone, which entails a further drawback to the user since, with a sudden motion by the tool, the latter may move out of its ideal sharpening position.
In U.S. Pat. No. 2,898,709, a knife sharpener is described comprising a grindstone with an angled outer surface, affixed to an engine which, in turn, is attached to the base. The sharpening motion is performed in the front portion of the casing, which comprises a support on which the tool to be sharpened rests. As in the above mentioned patent, the user may inadvertently move the tool out of the ideal sharpening position and even come into contact with the grindstone during sharpening.
U.S. Pat. No. 5,735,732 shows a drill sharpener comprising a grindstone that, in this case, is positioned parallel to the sharpener base. Thus, in order to get the drill sharpened, the user couples the drill to front and side housings on the sharpener casing which have a predetermined angling for sharpening said drill.
In U.S. Pat. No. 6,398,633 B1, a two-stage knife sharpener is described comprising three fixed grindstones lying on the same plane, the central grindstone being overlapped with a portion of the other grindstones. The tool to be sharpened is then placed in the two intersections of the three grindstones mentioned above, thereby providing for the two-stage sharpening motion. In this patent, the grindstone is also in contact with the user, as in the aforementioned patents. Likewise, the present patent sharpener does not have an ideal sharpening angle, which is not ideal for an unskilled user.
Additionally, Canadian Patent 1, 124, 080 shows an electric knife sharpener comprising, as in the aforementioned patents, a grindstone fixed to the sharpener base via an engine. The upper portion of the sharpener casing has differently angled slots for sharpening the tool against the grindstone front, rear and upper portions.
The Patent Application PI 0400199-0, which belongs to the inventor of this application, shows a single grindstone sharpening assembly having a flexible rod connecting the grindstone-engine assembly to the sharpening assembly base. Such rod is attached to the assembly base, the rod being responsible for the flexing. The disadvantage of such configuration is that, depending on the assembly storage form, the weight of the engine deforms the flexible rod, and, consequently, offsets the grindstone relative to both slots of the casing. Therefore, the rod remains permanently deformed in a predetermined position, which leads to the non-utilization of the assembly.
Patent Application PI 0401761-7, also belonging to the inventor of this application, further shows an electric sharpening assembly comprising, in addition to the prior art, a guide slot (steel plate) resulting in wear, and, among other problems, the locking of the tool to be sharpened.
Finally, Patent Application PI 0401928-8, also belonging to the inventor of this application, additionally provides an electric sharpening assembly, with two adjustment bands fastened by screws that bring the tool to be sharpened towards the grindstone. Such a way of fastening makes the adjustment of the sharpening assembly by the user difficult.